Fuel cells used in vehicles and others use gaseous hydrogen. Since gaseous hydrogen is very large in volume, compressed hydrogen gas is used. The volume thereof is however still large for practical use, leading to space problems. Liquid hydrogen is smaller in volume than gaseous hydrogen. Holding liquid hydrogen is however difficult and not suited for practical use. Thus, use of hydrogen in the solid state has been being studied and developed to provide reduced volume and enhanced ease of handling. Hydrogen is used in the solid state by being stored in alloys. Such alloys are called hydrogen storage alloys. Hydrogen storage alloys repeat absorbing and releasing hydrogen.
A hydrogen gas sensor using such a hydrogen storage alloy is disclosed in patent document 1. The hydrogen gas sensor disclosed in patent document 1 comprises a substrate, a Pd—Ag alloy layer vapor-deposited on a surface of the substrate, and a thin film of Pd or Pt formed thereon.
The substrate disclosed in patent document 1 is however in the form of a plate. Accordingly, the layer of the hydrogen storage alloy, vapor-deposited on this substrate, provides an area of contact with hydrogen approximately equal to the surface area of the substrate. In light of recent years' demand for storage of a larger amount of hydrogen, an increase in the ability to store hydrogen is required.